This invention relates generally to the field of downhole cavity tools and more particularly to a cavity positioning tool and method.
Subsurface resources such as oil, gas, and water are typically recovered by drilling a bore hole from the surface to a subterranean reservoir or zone that contains the resources. The bore hole allows oil, gas, and water to flow to the surface under its own pressure. For low pressure or depleted zones, rod pumps are often used to lift the fluids to the surface.
To facilitate drilling and production operations, cavities are often formed in the production zone. The cavity allows the well bore to be more readily intersected during drilling operations and collects fluids during production operations. The collection of fluids allows pumps to be operated intermittently when the cavity is full, which reduces wear on the pump.
Short extensions called a xe2x80x9crat holexe2x80x9d are often formed at the bottom of the cavity to collect cuttings and other drilling debris. As the subsurface liquids collect in the well bore, the heavier debris falls to the bottom of the rat hole and is thereby both centralized and collected out of the cavity. To avoid being clogged with debris, inlets for rod and other downhole pumps should be positioned within the cavity above the rat hole. In addition, the pump inlet should be positioned fairly low in the cavity to avoid vapor lock (i.e., below the fluid waterline). Traditional methods of positioning the pump inlets, however, are often inaccurate and inefficient, leading to clogging or vapor lock and increased maintenance and operation costs for the well.
In accordance with the teachings of the present invention, a cavity positioning tool and method are provided that substantially eliminate and reduce disadvantages and problems with prior systems and methods. In particular, a cavity positioning tool efficiently and accurately positions pump inlets and other downhole devices within or relative to a cavity.
In accordance with one embodiment of the present invention, a cavity positioning tool is provided that includes a head piece adapted to receive a downhole string having a longitudinal axis. A plurality of blunt arms are coupled to the head piece. In operation, the arms are operable to be radially extended outward from a first position of substantial alignment with the longitudinal axis to a second extended position.
More specifically, in accordance with a particular embodiment of the present invention, the arms are pivotally connected to the head piece. In this and other embodiments, the arms extend in response to rotation of the tool. In the absence of rotation, the arms automatically retract by force of gravity.
In accordance with another aspect of the present invention, a device is positioned relative to a subsurface cavity by coupling the device to a plurality of blunt arms. The blunt arms are lowered in a substantially retracted position into the subsurface cavity through a restricted passageway. In the cavity, the blunt arms are radially extended outward from the retracted position to an extended position. The blunt arms are then rested on the floor of the cavity, in the extended position.
In accordance with still another aspect of the present invention, a method is provided for degasifying a coal seam by lowering an inlet of a pump through a well bore into a cavity formed in a coal seam. The cavity extends radially from the well bore. A plurality of arms are coupled to the pump inlet. When the pump inlet is disposed within the cavity, the arms are radially extended. The pump inlet is then lowered until the arms rest on a floor of the cavity, such that the inlet is in a lower part of the cavity and above a rat hole extending below the cavity. Fluids are collected in the cavity and removed with the pump. Gas is recovered through the well bore.
In accordance with yet another aspect of the present invention, a method is provided for degasifying a coal seam by lowering an inlet of a pump through a well bore into a cavity formed in a coal seam. The cavity extends radially from the well bore. A plurality of arms are coupled to the pump inlet. When the pump inlet is disposed within the cavity, the arms are radially extended. The pump inlet is then lowered until the arms rest on a floor of the cavity, such that the inlet is in a lower part of the cavity and above a rat hole extending below the cavity. The pump inlet and arms are rotated, while the pump inlets maintain the same relative position within the cavity. Fluids are collected in the cavity and removed with the pump. Gas is recovered through the well bore.
Important technical advantages of the invention include providing an improved cavity positioning tool and method. In particular, the tool includes arms that are retractable for lowering through a well bore to a cavity and extendable in the cavity to position a device within or at a set relation to the cavity. In one embodiment, the arms are extended by centrifugal force and automatically retract in the absence of centrifugal force. As a result, the tool has a minimum of parts and is highly durable.
Another technical advantage of the present invention includes providing a method and system for positioning a pump inlet in a cavity. In particular, the pump inlet is positioned in a lower portion of the cavity by extending arms that rest on the cavity floor above a rat hole. This position of the pump inlet significantly reduces clogging of the pump inlets and prevents the pump from inadvertently entering the rat hole. Additionally, this position minimizes vapor lock.
Still another technical advantage of the present invention includes providing an improved method for supporting a pump string extended from the surface to a subterranean zone. In particular, a pump string is supported from the floor of the cavity. This allows well head maintenance and other surface operations to be performed without pulling out or otherwise supporting the string from the surface.
Still another technical advantage of the present invention includes providing an improved method for removing solid-laden fluids from a coal seam or other subterranean zone. In particular, a pump inlet is coupled to a cavity positioning device with extending arms that rest on a cavity floor above a rat hole. The arms are rotated slowly to agitate the liquid in the cavity, thereby suspending debris to allow removal within the liquid and lowering the tendency of particulate matter to coalesce. Thus, the debris and particulate matter is less likely to form clumps of larger particles, which reduces clogging of the pump inlets.
Other advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.